An analysis chip having a substrate on which a selective binding substance such as genes, proteins, lipids, sugars or the like selectively binding to a substance to be examined is immobilized and in which the selective binding substance on the substrate is reacted with a sample to analyze the presence/absence, the state, or the amount of the substance to be examined contained in the sample has been known. As such a substrate, substrates made of glasses, metals, or plastics have been generally used.
As one aspect of the analysis chip, there is a microarray in which molecules such as DNA, proteins, sugar chains or the like are arranged on a substrate at high density to simultaneously measure a large number of gene expression of several hundreds to several tens of thousands. Use of the microarray enables detection and quantification of nucleic acids based on a hybridization reaction between nucleic acids/nucleic acids and detection and quantification of proteins or sugar chains based on specific reactions between proteins/proteins, between sugar chains/sugar chains, or between sugar chains/proteins. For example, the use of the microarrays allows systematic and comprehensive gene expression analysis in various disease animal models and cell biological phenomena to be carried out. Specifically, the use of the microarrays allows the function of gene, that is, the protein encoded by the gene to be clarified and the time when the protein is expressed and the site where the protein is affected to be specified. Searches for disease genes and treatment-related genes and searches for therapeutic methods can be carried out by analyzing variations in gene expression at the cell or tissue level of an organism using the microarray and constructing a gene expression profile database in combination with physiological, cell biological, and biochemical phenomenon data.
Among analysis chips, a DNA chip (or a DNA microarray) in which DNA is arranged on a substrate is used for nucleic acid detection, quantification and the like based on a hybridization reaction between nucleic acids/nucleic acids. As the DNA chip, a DNA chip in which a large number of DNA fragments are aligned and immobilized, for example, on a plane substrate made of glass at high density is used. The DNA chip is used to detect each gene or measure the amount of each of the genes in a sample. For example, the DNA chip is used at the time of measurement using a method of hybridizing a sample in which the expression gene of research target cells is labeled with a fluorescent dye or the like on a flat substrate and binding nucleic acids (DNA or RNA) complementary to each other to rapidly read the fluorescent light at the site by a high resolution detection apparatus (a scanner) or a method of detecting responses such as electric current values based on an electrochemical reaction. In addition, the DNA chip is highly expected to be applied not only to gene expression analysis by detecting and quantifying expressed genes but also in application fields such as detection of the single nucleotide polymorphism (SNP) of genes.
In addition, the analysis chip is used as an inspecting and analyzing means for not only the nucleic acid such as DNA, but also proteins, saccharides and the like. In particular, proteins such as antibodies, antigens, enzyme substrates and the like are immobilized on a substrate in an analysis chip for protein.
In recent years, efforts to realize inspection and diagnosis by genes and proteins have been actively carried out using analysis chips including the above DNA chip. When the analysis chips are used for mass screening such as health checks and comprehensive medical examinations, the number of samples to be processed becomes enormous and thus a system capable of measuring a large number of samples at a time is essential. For this reason, development of an analysis chip capable of inspecting a plurality of samples with one chip has been developed.
In a reaction step carried out after a sample is dropped, for example, when the sample spills out from the reaction portion, the spilled sample may cause contamination with the adjacent reaction portions in the analysis chip having a plurality of reactive portions to which the selective binding substance is immobilized. To solve this problem, an analysis chip in which the sample contamination to the adjacent reaction portions is avoid by surrounding and partitioning the outer periphery of each of the reaction portions with a water repellent material has been devised (for example, refer to Japanese Patent No. 4856057).
Specifically, JP '057 discloses a probe array in which a detachable sheet-like separator partially having a water repellent region is provided to prevent the sample contamination among adjacent reaction portions. As a reason for the detachment, it is described that the chemical properties of the substrate surface can be uniformly retained by attaching a separator after treating the substrate surface. The separator can be detached at the time of washing and signal detection.
As described above, the analysis chip in which the outer periphery of the reaction portion is partitioned by the water repellent material can avoid sample contamination to the adjacent reaction portions. On the other hand, in the analysis chip, a labeled substance that is unreacted (unreacted labeled substance) having strong hydrophobicity may adhere to the water repellent material after the reaction. In JP '057, a large amount of the unreacted labeled substance adheres to the separator because the entire surface of the analysis chip surface other than the reaction portions is a water repellent surface due to a sheet-like separator. In general, the analysis chip is washed by immersing the analysis chip into a washing liquid one time or more times and thus a large amount of the unreacted labeled substance adhering to the chip is in a state of being floated in the washing liquid after the immersion when the analysis chip is treated in the subsequent washing process in a state where a large amount of the unreacted labeled substance adheres. When the analysis chip immersed in the washing liquid is taken out, the unreacted labeled substance does not adhere to the separator because the washing liquid on the separator runs out, while the washing liquid containing the unreacted labeled substance remains on the reaction portions having hydrophilicity without running out. The unreacted labeled substance remaining on the reaction portions remains in the reaction portion in a dried state after the subsequent centrifugal drying process and the remaining unreacted labeled substance may act as background noise at the time of inspection. Therefore, an analysis chip capable of reducing generation of the background noise due to the remaining unreacted labeled substance and obtaining accurate analysis result is desired.
It could therefore be helpful to provide an analysis chip capable of reducing generation of the background noise generated after washing.